For words that only have three letters, there's no 4th letter. As an example with the word “add”, there isn't any a lot more letters afterwards and so need to be the word "insert". The word “addict” is while in the BIP39 wordlist however you might have used “addi” for https://social-lyft.com/story8699287/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting